1. Field of the Invention
This invention relates to skis utilized in Winter sports, and adapted to slide on snow and ice.
2. Related Applications
The following copending applications disclose subject matter related to subject matter in the present application:
Ser. No. 156,962 filed Feb. 18, 1988; PA0 Ser. No. 157,467 filed Feb. 18, 1988; PA0 Ser. No. 194,147 filed May 16, 1988 (P6373); PA0 Ser. No. 194,129 filed May 19, 1988 (P6374).
3. Description of Background and Relevant Information
A ski generally comprises a lower sliding surface having an angle iron on each lateral edge for gripping snow, two lateral surfaces defining the width of the ski, and an upper surface having binding means located in a central binding zone by which a user attaches his boot to the ski. The front or leading end of the ski is curved upwardly to form a spatula; and the ski is relatively narrow in width compared to its length which defines a longitudinal direction. The lower surface of the ski defines a contact zone located between a front contact line and a rear contact line.
In conventional skis, the thickness of the body of the ski varies along the length of the ski in the longitudinal direction having a maximum in the central binding zone where the flexional movements are a maximum during the use of the ski. In this zone, internal flexion couples are greatest during the use of the ski. Because the thickness of the ski in the central binding zone is a maximum, and the thickness near the front and rear ends is a minimum, a uniform load distribution is achieved as disclosed in French Patent No. 985,174, for example.
Conventional skis have a composite structure in which different materials are combined in a manner such that each composite operates in optimal fashion taking into account the distribution of the mechanical stresses. The composite structure comprises resistance or reinforcing strips of a material having a high mechanical resistance to strain and substantial rigidity so as to resist flexional and torsional stresses produced in a ski during its use. The conventional structure usually includes filler material, and sometimes shock absorption strips.
The two principal composite structures finding current wide scale application in skis are the so-called sandwich and casing structures. In a typical casing structure, such as described in French Patent No. 985,174, and FIG. 3 of French Patent No. 1,124,600, the ski comprises an internal core made of cellular material which may be partially hollow, and mechanical resistance strips surrounding the core in the form of layers that constitute a casing for the core.
In a typical sandwich structure, such as described in U.S. Pat. No. 4,405,149, the ski comprises a central core formed from cellular material which can be partially hollow, and reinforcements on its upper and lower surfaces formed by resistance layers having requisite resistance and rigidity properties greater than those of the core itself. Typically, discontinuous strips of prestressed viscoelastic material are bonded to the core along two or three separate longitudinally spaced zones. At least one of these zones is near the spatula of the ski, and another of the zones is located adjacent the binding zone. Swiss Patent No. 525,012 discloses longitudinal strips formed of viscoelastic material bonded to the upper surface of the ski to form a sandwich structure.
In all of the known skis using a sandwich construction in which the shock absorption strips are formed of viscoelastic material, both the core and the strips have a uniform width along their entire length. When the strips are positioned substantially over the entire length of a ski, it has been found that skiing comfort is improved, but that the gripping and holding power of the ski during turning maneuvers are reduced. In efforts to solve this problem, it has been proposed to limit the length of the shock absorber to the front half of a ski, i.e., to the zone between the spatula and the binding zone. Such an expedient, however, appears to provide no advantage over a construction in which the shock absorber extends over the entire length of the ski. Finally, in the case where the strip is segmented or divided into a plurality of separate segments, as is described in U.S. Pat. No. 4,405,159, the shock absorption effect is reduced, and the influence of the segments becomes practically negligible at the frequencies of vibration produced in the ski under normal use when a boot is attached to the ski by a binding.
Furthermore, in conventional skis using a sandwich construction, the shock absorption element constitutes a supplemental element which complicates the manufacture of the ski and substantially increases its cost.
An object of the present invention, therefore, is to overcome the disadvantages of known ski structures and provide a ski whose shock absorption properties are such as to produce a remarkable increase in both comfort and technical performance.
Another object of the invention is to confer to the body of the ski, a shock absorption property which is a non-constant function of the length of the ski. A further object of the present invention is to obtain a desired non-constant distribution in the shock absorption properties of a ski without major modification of its structure in order to achieve homogeneity of structure and behavior, and good distribution of reactions along the length of the ski thus providing the user with an impression of comfort and regularity in the reactions of the ski to its travel on snow.